Ronn W

Scratch marks

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I am trying to finish a curly maple box top  (8" x 6") with shellac.  Never had this problem before.  There are fine scratch marks or ridges parallel to the grain.  You can only see them when looking almost paralle with the grain and the light is jsut right but they are there.  So I sanded it down with 400 grit until the entire surface was the same sanded texture ( no shiny streaks).  I brushed on a new coat of shellac - the streaks were back. { I am using a  damned expensive 3/4" sable brush).  I decided to put 2 more coats on and then sand it smooth again.  That done, I swithed to spray shellac from a can - the marks are back.  My conclusion is that it was not the brush leaving the marks.  So it must be sanding marks from the 400 grit sandpaper.  So what should I have done differently when I sanded back - finer sand paper?  circular or random sanding pattern.? 

I should note that I had the same streaks on the walnut sides of the box but they diappeared after sanding back and applying a couple of coats with the brush.  Maybe they are still there but I just can't see them on the walnut.

I have test piece of curly maple and will keep experiementing but I would appreciate any thoughts.

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Drum sander can leave parallel scratches, coarser grit deep scratches can remain if you skip grits. When I go from the drum sander to the random orbit I go one grit coarser, 150 drum then 120 ROS for example. Then 150-180-220 etc. 

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Was the stock rough sawn & you planed it ? If it was S2S they could have used a drum sander to dress the stock. Or it could be something else entirely........

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Are the scratches all in the same direction you were sanding? Is there a chance that your 220 grit sheet picked up something and caused them?

You could try building some heavy coats and then trying to sand back to smooth. That seems like a lot of work and doesn't solve the cause of your problem.

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8 minutes ago, Chestnut said:

You could try building some heavy coats and then trying to sand back to smooth. That seems like a lot of work and doesn't solve the cause of your problem.

Shellac does not build up. It won't fill any gap.

Remove the shellac with alcohol/scraping  and go back to sanding or smoothing.

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10 minutes ago, Immortan D said:

Shellac does not build up. It won't fill any gap.

Ahh so then why would any one ever suggest applying more than 1 coat?

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Just now, Chestnut said:

Ahh so then why would any one ever suggest applying more than 1 coat?

Each extra coat mixes with the previous one. You polish a coat, then apply a new one.

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No. When you apply a new coat of poly it builds a new layer. That does not happen with shellac. Each subsequent coat is just dissolving the previous coat and mixing a bit more shellac into it.

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There are actually folks who use shellac as a pore filler.  I find the process too laborious for the result.  This filling function is for pores and will not hide scratches . . . does anything hide scratches besides paint :rolleyes:.  Be that as it may I do use a fair amount of figured woods and the same thing that makes them look wonderful means that there is little consistent direction figure.  This means you are sanding across the grain more than when sanding less figured material.

57cf30399b8f5_Picboxesround2(24).jpg.6fdcf6e9f75422d068ad7a2beaceef87.jpg

Not skipping grits is a basic and we all do that if we want a good result.  Sanding enough with each grit to eliminate the previous scratch pattern is a must and it is easy to let things slip by if you are not using a raking light inspection between the grits; at least between some of them anyway.  If you see scratch lines left behind from the previous grit, go back and fix that . . . the next finer grit will not take care of it for you ;-)

57e68fb06a01a_GnGLowCoD(276).jpg.21c9c11dc776bdc6d2307a6de757dfec.jpg

 

I sand to 400 and beyond depending on the material.  For curly, tiger and random wavy patterns I use a sponge as my "block" and sand as if tracing the pattern.  Bird's Eye can be problematic since the irregularities, that we love so much, are quite small.  Here I often switch to a very fine grit flap sander, steel or non-woven wool, etc. 

Certainly the best way to save time and effort is to put out a little extra effort during the process.  Use a raking light, wipe the surface with mineral spirits to accent any flaws, step back a grit and repeat the area if flaws are detected.  A general habit I developed for sanding is to sand with each grit level until you think your done . . . now sand that much again.  I seldom need to go back and fix things anymore.  You will save time (and certainly frustration) in the long run. 

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31 minutes ago, gee-dub said:

Use a raking light, wipe the surface with mineral spirits to accent any flaws, step back a grit and repeat the area if flaws are detected.  A general habit I developed for sanding is to sand with each grit level until you think your done . . . now sand that much again.  I seldom need to go back and fix things anymore.  You will save time (and certainly frustration) in the long run. 

Raking light?  Do you use a special light or just any bright light held at a relatively flat angle?

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5 hours ago, Immortan D said:

No. When you apply a new coat of poly it builds a new layer. That does not happen with shellac. Each subsequent coat is just dissolving the previous coat and mixing a bit more shellac into it.

Never said anything about multiple layers.

From what Ron was saying i assumed the scratches were in the finish not the wood.

 

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1 hour ago, Chestnut said:

You could try building some heavy coats and then trying to sand back to smooth

 

6 minutes ago, Chestnut said:

Never said anything about multiple layers.

Oh, I see.

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I use LED exterior spotlight bulbs (90 watt equivalent ) in those swing arm architects lamps to provide raking light in my shop.  They used to be expensive & heavy bulbs but the newer ones by Feit are  lighter & around $18 for a 2 pack. Bright White "True & Natural " 90+color rendering index. Tertial lamps at IKEA are $13.

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Since I posted I have sanded the surface again with 400 grit using light circular motions and I am sure that the surface was smooth when I was done.  I then re-sprayed and the lines are still there.  I am convinced that the lines are in the wood and at I am seeing them through the shellac.  My separate test piece shows no such lines and I have resanded and re coated it in various ways.  I never did sand all the way way back to the wood, ie, start completely over.  I supposed that I could use some steel wool to dull the finish a little and make the lines less visible but, I really don't want that look for this box.  More attention to the wood prep next time. 

Thanks for all your input.

"The fault, dear Brutus, is not in our stars but in ourselves that we are underlings." -----

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1 hour ago, Ronn W said:

"The fault, dear Brutus, is not in our stars but in ourselves that we are underlings." -----

Wow Ronn, that is some serious culture showing through.  Way to go.:)

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I agree, if you're trying to achieve an extremely smooth finish you can't always see some of the scratch marks until you get to the finer grits.

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10 hours ago, Ronn W said:

Some times scratches will not show up until the polishing process reaches a certain level of sheen and then, poop,  that scratch shows up.

I understand but it lost a ltille in translation:wub:

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Disclaimer; not a finishing expert.  just a hack with lots of practice :).

On 12/5/2017 at 7:54 PM, Ronn W said:

I am trying to finish a curly maple

Curly material can be tricky.  The hard/soft portions of the material that makes it wonderful also make it challenging.  220 is pretty course for a figured wood in my experience; depending on the result you are after.  You can watch Charles Neil (who I think does some really nice stuff) use 180 to 220 and state that they rarely go higher.  They also have professional top coat spray products and methods that I do not have. 

With tiger or curly maple there is little chance of burnishing the surface with too fine a grit, the curls are too soft.  Your sanding block becomes pretty important with curly material.  A ROS or small sanding block will ride up and down the hard and soft areas.  A large block (think about your No.7 hand plane) will ride on the hard portions over the soft portions and bring things into an even plane.  I flooded this surface with shellac after sanding; I flooded because I wanted the shellac to be carried deep into the soft material:

1831144754_KelloggInspiredWallCab(167).jpg.37b5a7c3a7b8404c0eb5456bd897d525.jpg

I followed this with 400 - 800 between coats to get here:

809927945_KelloggInspiredWallCab(173).jpg.1980c63393e2951400c36264ee600183.jpg

220 grit is made up of about 68 micron particles that leave 30+ micron deep scratches; easily visible with the naked eye.  There are heavy film finishing techniques that will provide a good surface appearance over even deeper scratches.  There is nothing wrong with this. 

I like to see 'into' the wood on my pieces and so keep my top coats pretty clear. I have learned that, for me, when I see scratches after starting the finish process . . .  I stop.  Once the finish is dry or cured, I continue the sanding, scraping or whatever surface prep protocol I am using to eliminate the scratches.  This may or may not require stripping depending on the finish product I have started to use.  General rule; if it looks good with mineral spirits wiped on under a raking light, it will look good with the finish applied.  It is a quick easy "insurance policy" that is well worth taking the time to do.

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On 12/6/2017 at 8:44 AM, Immortan D said:

Shellac does not build up. It won't fill any gap.

Remove the shellac with alcohol/scraping  and go back to sanding or smoothing.

It will build up thickness as you apply more but it gallows the contour of the coat before it because each coat dissolves the coating under it. Causing one solid layer of finish.

 

So you are correct in saying its won't fill a gap. At least not like a varnish or poly would.

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